1. Field of the Invention
The present invention relates to a method for manufacturing plates consisting of thermoplastic synthetic material or the like by compression molding and to apparatus for practicing the method.
More specifically, a mold consisting of a respective horizontally-disposed upper portion and lower portion is first filled with synthetic base material in granule form or the like, is heated while being charged with pressure and closed for the purpose of melting the synthetic base material. Finally, the mold is cooled while being pressure-charged in such a manner that the cooling essentially occurs proceeding from the horizontal mold surfaces. As indicated above, the mold comprises a bipartite, heatable and coolable mold which is disposed essentially horizontally and whose upper portion and lower portion are movable relative to one another while being pressure-charged with controllable mold pressure in two stamp presses or the like respectively exhibiting essentially planar upper and bottom platens. The platens of the one press are only heatable and the platens of the other press are only coolable and the mold with the upper or lower portion is designed separate from the platens and is successively insertable into the hot press and into the cold press. A conveyor for introducing the mold filled with the synthetic base material into the hot press, for forwarding the same into the cold press after conclusion of the melting operation, and for delivery of the mold out of the cold press, is provided for execution of the corresponding steps of the method.
2. Description of the Prior Art
Filter plates of the type generally set forth above, which can be combined in groups to form the filter presses are usually manufactured of thermoplastic material. Heretofore, one has proceeded such that a heavy-duty press is employed, its upper and bottom platen being respectively designed as both a heatable and coolable lower portion and upper portion of the compression mold, whereby devices for heating the narrow sides of the filter plate to be manufactured during the cooling operation are additionally provided. The cavity of the mold is essentially completely filled with synthetic granular material such as polypropylene or the like. Given such a procedure, it is necessary to exert rather significant pressures on the synthetic material during the heating operation and, in particular, also during the cooling operation, such pressures being exerted with a structural expense for the presses caused by so doing since a warping of the filter plates or the like to be manufactured or, respectively, the occurrence of irregularities or bubbles could otherwise not be prevented. Such molding presses are not only expensive to manufacture, but the known methods are also very energy intensive, due to the fact that considerable masses must be heated and cooled whereby the counter-heating required during the cooling operation further produces an additional energy loss. Moreover, the channels for flow agent present in the bottom and upper platens of the presses must be designed such that they are suitable both for conducting a heating agent and then a cooling agent, so that a considerable structural expense results therefrom.
From the known German published application No. 30 01 172, fully incorporated herein by this reference, a method and apparatus of the type initially mentioned are provided wherein a mold frame limiting the filter plate to be manufactured is employed, the mold frame being later discarded, whereby flat insulating strips can be placed below the mold or, respectively, on the heating or cooling plate.